Sure they shouldn't have to, but they chose to do it anyway. Just in case someone would think they condoned this promoted commencement speak where one of their decorated players was speaking. They put out a brief message to make it clear they are not expressed views of the NFL. Why would this upset anyone?
When Kaepernick took a knee and the NFL didn't say anything there were people saying they would boycott the NFL. They didn't say "well, that's the player's views and not the NFL."